Automatic voltage compensator for three phase



July 23, 1963 A. M. sclAKY 3,098,977

AUTOMATIC VOLTAGE COMPENSATOR FOR THREE PHASE Original Filed Dec. 2, 1958 3 Sheets-Sheet 1 LINE I/UL THGE #295 g PR/MAkY July 23,' 1963 A. M. SCIAKY 3,098,977

AUTOMATIC VOLTAGE COMPENSATOR FOR THREE PHASE Original Filed DSG. 2, 1958 5 Sheets-Sheet 2 D62 7,4 WUI/ND SECONDA/1:71515' INVENT OR.

July 23, 1963 A. M. sclAKY 3,098,977

AUTOMATIC VOLTAGE coMPENsAToR FOR THREE PHASE Original Filed Dec. 2, 1958 3 Sheets-Sheet 5 7629.3 96 "VY m E75 ZVZ ZZ 7/ 75 26d 260 85 am E5 325 dg 32E .325 Z55 262 INVENT OR.

United States Patent() 9ll,lll7

6 Claims. (Cl. 328-69) The invention relates tot automatic voltage compensators embodying improved phase shift means for three phase alternating circuits, and has reference more particularly to apparatus of this nature which will automatically compensate -for voltage variations in the alternating power supplied to welding machines so as to maintain the welding current at a constant value for any particular lheat setting.

Welding system-s have been provided with phase shift control means wherein a particular value of welding current is obtained by shifting the tiring point of the ignitrons which, in turn, controls flow of the primary current to the welding transformer. Such phase shifting networks have generally required manual adjustments although some welding systems in the past have been provided with phase shifting networks which control the welding current by automatically adjusting the firing point of the ignitrons in such manner that it is a function of the line voltage or the welding current being produced.

ln the present invention the variations in the voltage of the supply current are compensated for automatically by providing a voltage wave form which is synthesized from the voltage of the -supply current so that its magnitude is proportional to lthe output of the welding machine at every phase angle in the range of firing angles of the said machine. For each cycle a tiring pulse can be produced at the moment the voltage wave form reaches some predetermined pre-set value.

lf the pre-set value is kept constant by means of a voltage regulator tube, a drop in line voltage will advance the ring angle and conversely an increase in line voltage will retard the firing angle, thus keeping the secondary welding current of the machine substantially constant.

An object of the invention is tol provide an improved voltage compensating circuit for three phase which will incorporate new and novel electronic circuits lhaving operation to produce firing pulses for each phase and at the proper phase angles so as to compensate for voltage varia tions in the three phase power source. ,f

More particularly, according to the invention, the alternating current voltages of the three phase power supply are applied to a transformer, andthe pulses from each secondary winding are iiltered by resistance-capacity networks, then amplified and combined by means of a pushpull cathode follower. The output obtained from a split secondary of the cathode follower transformer is superimposed on a variable direct current voltage obtained by rectifying the alternating current supply voltage and the lsame constitutes the synthesized wave forrn as produced for a particular phase of the power supply.

A further object of the invention, based on lthe foregoing, is to provide a voltage compensating circuit having particular application to three-phase welding machines and wherein the tiring angles are obtained by an adjustable reference voltage which, for any adjusted position, will determine the level on the synthesized wave forms at which the tiring pulses will be produced.

With these :and various other objects in view, the invention may consist of certain novel features of constructionand operation, as will be more fully described and A Patented July 23, 1963 ICC particularly pointed out in the specification, drawings and claims appended thereto.

In the drawings which illustrate an embodiment of the device and wherein like reference characters .are used to :designate like parts- FIGURE `l is a schematic diagram illustrating the shape of a synthesized wave form Ifor a half cycle of conventional alternating voltage;

FIGURE 2 is a Wiring diagram showing a delta connection for the primary winding of a three-phase transformer as employed ,for the compensating circuit of FIGURES 3 yand 4;

FIGURE 3 is a schematic wiring diagram illustrating in part a preferred embodiment of a three phase voltage compensating circuit coming Within the invention;

FIGURE 4 is a schematic wiring diagram illustrating additional circuit connections which supplement those of FIGURE 3 to complete the three phase voltage compensating circuit; and

FIGURE 5 is a wiring diagram schematically showing a preferred circuit arrangement for applying firing pulses to a three phase welding machine.

Referring in particular to FIGURES 2, 3 and 4, it will be understood that the compensating circuit of the invention employs a three-phase delta connected transformer 160. Said transformer has at least two secondary windings for each primary Winding, and the secondary windings have electrical connection with cooperating circuit means for producing the synthesized wave forms, including the alternating current and the direct current components, and for also producing the direct current voltage level which determines the phase shifted tiring angles for the ignitrons of the welding machine.

It is first of all necessary to synthesize voltage wave forms from the alternating current voltages supplied by the power lines. The magnitude of each Wave yform will be proportional to the output of the Welding machine at every phase angle in the range of tiring angles of the machine. Such a synthesized wave form is illustrated diagrammatically in FIGURE 1. Although it is difficult .to ,determine theoretically the required Wave forms for three phase welding machines because of the non-linear characteristics of the iron in the transformer, it can be stated that the main objective is to produce a constant average current in the load, notwithstanding the variations in the source current. It is, therefore, necessary that the ring angles -be such that the area onder the voltage curve of the source current will be constant.

The three phase transformer 160, FIGURE 2, .includes three primary windings 161, 162. and 163 connected in delta across the three phase alternating current supply lines L1, L2 and L3, respectively. 'Ilhe lsecondaries for the three-phase transformer i60, vas shown in FIGURE 3, consist of two sets of Idelta connected windings, such as 165 and 166, `and one set of star connected windings 167. Considering first the set of windings 165, it will be seen that the same consist of secondaries 168, 169 and 170 connected in delta and having the conductors 171, 172 and 173 joined to certain taps on the windings, respectively, which accomplishes a phase-shifting of the line voltage approximately fifteen degrees in advance of normal. In a somewhat similar manner the set of windings 166, consisting of the lsecondaries 174, 17S and 176, is likewise delta connected, and the conductors 177, 178 and 179 are joined thereto at certain taps to accomplish a retarded phase-shifting of the li-ne voltages approximately fteen degrees. The reason for the particular tap connections to the delta connected secondaries is to produce `a high frequency ripple inthe rectified direct current output of the rectifier generally designated by numeral 180, to be presently described in detail. As a result of the high lfrequency ripple, which is in this case seven hundred and twenty per second, a direct current is obtained which has very little fluctuation, and which in addition will vary as the amplitude of the supply Voltage may vary. This is an important feature of the invention, since as the rectified voltage varies the synthesized waveforms will shift their position relative to the direct current reference level, thereby either advancing or retarding the ring angles.

The rectiiier 188 includes the potentiometer 181 and the connecting conductors 182 and 183. ln addition to the condenser 184 a plurality of series-connected reotiiiers, such as 185 and 186, are connected across the conductors in parallel relation and accordingly the llow of current as permitted by the rectifiers is from the negative conductor 182 to the positive conductor 183. Since the secondary winding leads 171, 172 and 173 for the secondary 165, and the leads 177, 178 and 179 for the secondary 166 are connected at 187 between each of the rectiers 185 and 186, the system will deliver a direct current out-put having a high frequency ripple :of small uctuations and wherein the magnitude of the voltage will vary as the polyphase power supply may vary in voltage. The said output of the rectifier 180 comprises the direct current component of the synthesized waveforms, as will be fully understood as the description proceeds.

The third set of secondary windings for the transformer 160 comprises a six-phase star connection and the same is produced by joining the center taps of three secondary windings to la common terminal. For example, the windings 191A and B are joined to the common terminal 190 as are also windings 193A and B and windings 195A and B. The conductors 197 and 198 connect the windings 191A and B through the resistors 216 and 217 to the grids 200 and 201, respectively, of an electronic tube 202 generally referred to as a cathode follower. The tube is of the dual triode, hot cathode type such as a 6463 which is characterized by a low internal voltage drop when conducting. The tube 202 has two plates 203 and 204 land two cathodes 206 and 207. 'Ihe tube is connected `for push-pull operation and accordingly the two cathodes are joined to a winding 208 which is center tapped by the conductor 210 which connects with the negative conductor 211 of the direct current source. The positive conductor 212 of the direct current source is connected by means of conductors 212 and 214 to the plates 203 and 204 of the cathode follower tube 202. The conductor 2110, which center taps the winding 208, is joined by means of conductor 215 to the common terminal 190 of the six-phase star connected secondary.

Referring again to the conductors 197 and 198, it will be seen that they each feed a resistance capacity lilter located in advance 'of the grids and which includes the series connected resistors 216 and 217 and the condensers 218 and 219, each condenser being connected on one side of the junction of the resistors 216 and 217 land on the other side of the center tap 190. Since it is diflicult to select components for the resistance-capacity filters having identical values, it will be understood that the wave forms from windings 191A and B, as delivered to the grids 200 and 201, may not be precisely one hundred and eighty degrees opposed. However, any `discrepancy will be taken care of by the cathode follower system so that the wave forms delivered by the secondary of windings 208A and 208B will have a polarity which will be precisely opposed to each other.

Windings y193A and B are similarly connected by con-- ductors 220 and 221 to the grids 222 and 223, respectively, of the cathode follower tube 224. 'lhe plates 225 and 226 of the said tube are joined by conductors 227 and 228 to the positive conductor 212 of the direct current source. The cathodes 230 and 231 connect with the winding 232 which is center tapped by conductor 233 and connected thereby to the negative conductor 211 of the direct current supply. The resistance capacity lters for the grids 222 d.. and 223 include, respectively, the series connected resistors 234, 235 and the condensers 236 and 237. The center tap conductor 236 is joined by conductor 215 to the common terminal P of the six-phase star connected secondary.

The windings A and B have connection by means of the conductors 240 and 241 to the grids 242 and 243, respectively, of the cathode follower tube 24,4. The plates 245 and 246 are connected by conductors 247 and 248 to the posit-ive side of the direct current source. The cathodes 250 and 251 are connected to the winding 252 which is center tapped by means of the conductor 253 having connection with conductor 211 comprising the negative side of the direct current source. The resistance capacity filters for the grids 242 and 243 include the series connected resistors 254, 255 and the condensers 256 and 257.

The windings 208, 232 and 252 of the cathode followers 202, 224 and 244 comprise the primary windings of three transformers, namely, 268, 278 land 300, and which have inductive relation with secondary windings, respectively, as illustrated in FIGURE 4. Considering first the winding 208 which is center-tapped so that the sarne is divided into two windings 208A and B, it will be seen that the secondary for the same consists of a winding 261 which is likewise center-tapped to form a pair of windings, namely 261A and 261B. Accordingly, when a voltage from the :alternating current supply line is impressed on the primary winding 161` of the delta connected transformer 160, similar voltages are induced in the secondary windings 191A and B and these rare accordingly fed to the resistance-capacity filters associated with the cathode follower 202 and which drive the follower so that voltages are devoloped in the cathode-plate circuit thereof which includes the windings 208A and B. As previously explained, the voltages in said windings are opposed to one another. The inductive relation which the secondary winding 261 has with the primary winding 208 will induce in the secondaries 261A and 261B similar electric voltages which are now exactly one hundred and eighty degrees opposed. The said voltages are supplied by conductors 262 and 263 to the grids 264 and 265 of the electronic tube 266. Said tube is preferably a 12AX7 of the dual triode, hot cathode type, the same having a high mu :and sharp cutoff characteristics. The said tube includes ya pair of plates 267 and 268 and la pair of cathodes 269. The cathodes are suitably connected to the negative conducrtor 211 of the direct current 4supply source, whereas, the plates are connected to the positive conductor 212. The connection including ltering circuits such as the resistor 270 and condenser 271 for plate 267 and resistor 272 and condenser 273 for plate 268. Also connected in circuit with plate 267 is a primary winding 274- for a transformer designated by nurnenal 275 and in a similar manner primary winding 276 of transformer 277 is included in the circuit with plate 2681.

The cathode follower tube 224 having the winding 232 in its plate-cathode circuit will likewise produce voltages in windings 232A and 232B in response to those developed -in the primary winding 162 of the delta connected transformer 160. The winding 232 comprises the primary of 'transformer 278, having a secondary winding 280, the same being center-tapped to form a pair of windings 280A and B. Through conductors 281 and 282 the voltages from winding 280 are fed to t-he grids 285I and 284, respectively, of an electronic tube 285 having plates 286, 287 and cathodes 288. The circuit to plate 286 includes a resistance-capacity lilter formed by the resisto-r 290 and the condenser 291. Also the primary winding 292 of a transformer 293 has connection in the said plate circuit. Plate 287 is similarly connected to a filter formed by resistor 294 .and condenser 29S. The winding 296 is in circuit therewith and the same comprises the primary winding of a transformer 297.

The voltages produced in winding 252 of the cathode follower 244 are in response to voltages developed in the winding 163 of the delta connected transformer 160. Since winding 252 is center-tapped the voltages in 252A and 252B will be opposed. Winding 301 of transformer 300 has inductive relation with winding 252 Iand the same is center-tapped as shown to form windings 3011A and B. By means of the conductors 302, 303 the voltages from said secondary windings are delivered to the grids 304, 305 of an electronic tube 306. ySaid tube includes plates 307 and 308 and a pair of cathodes 309. The resistor 310 and condenser 311 form a resistance-capacity iilter in the circuit with plate 3017, the circuit also including primary winding 312 of transformer 313. The resistancecapacity filter for plate 303 includes the resistor 314 and condenser 315. The primary winding 316 of transformer 317 is also included in the circuit to said plate.

It will be understood from the foregoing that the output transformers of the cathode followers produce the alternating current component of the synthesized waveforms and it will be further understood that the salmeis applied to the grids of the electronic tubes 266, 285 and 306. The plate circuits of .these tubes include the primary windings of transformers such as 275, 277 for tube 266, transformers 293, 297 for tube 285, and transformers 313 and 317 for tube 306. The primary windings for these transformers develop electric pulses across their tenminals whenever their associated tube is driven from cutoff to conduction or vice versa. r[he pulse is 'of one polarity when the tube is driven from cutoff to conduction and is of the opposite polarity when driven from conduction to cutoff. s

A secondary winding is associated with the primary winding of each transformer, as shown in FIGURE 5, and the same is connected in such la way lthat a positive pulse is produced when the tube is driven from cutoff to conduction. The pulses therefore comprise the six tiring pulses required lfor firing the ignitrons of the three-phase welding machine. For a more particular disclosure of the manner and circuitry such as may be employed in triggering the `ignitrons :of the welding machine reference is made to the Solomon Patentr2,600,519, granted June 17, 1952 and entitled Sequence Control Circuit and Timer.

The reference voltage, as previously explained, can be preset and its particular setti-ng determines the firing angles for the voltage compensating circuit. In the schematic `diagram of FIGURE 1 it will be seen that the direct current reference voltage has been set so as to produce tiring pulses which are phase-shifted. Although the direct current voltage reference level remains fixed, it will be observed that the direct current voltage of the rectifier 180 will vary in value according to variations in the voltage of the alternating currents supplied [to the three-phase delta connected transformer 160. Accordingly, the synthesized warefonms :are shifted in position with respect -to the reference level and the tiring angles lare either advanced or retarded to compensate for the line voltage variations. v

The direct current for the cathode followers 202, 224 and 244 and for the electronic tubes 266, 285 and 306 is obtained from the alternating current supply source through transformer 320i having the secondary winding 321 and which is center-tapped by conductor 211, which accordingly forms the negative side of -the direct current source. The rectifiers 324 kare in ycircuit with winding 321 and the Same form therewith a full wave rectifier, the output of which is supplied to the positive conductor 212 of the system. The condense-rs 323 and 325 are connected in parallel across -the direct current source and byrneans of conductor 326 the negative side of the direct current source is connected to the low limit potentiometer 327. 'Iheregulator tube 328 has connection to resistor 322 and the combination is connected across the source of direct current. The regulator tube is gas filled and is of the cold lcathode type. `In operation the same ywill supply a fixed output voltage irrespective of voltage changes as regards the supply current and irrespective of any changes which may take place in the load. The conductor 331 joins the tube to the high limit potentiometer 332. To provide for adjustment of the direct current voltage reference level a volt-age divider 334 is provided which is of la type to give Vernier control with no gaps. The resistors 335 are connected to potentiometer 327. lIn -a similar manner resistors 336 are connected to potentiometer 332. The 4dividers 337 are adapted to make selective connection with resistors 335 and 336 so that `as the resistors 335 are added the circuit resistors 336 are cut out. The dividers have connection respectively to the terminals of the potentiometer 338 and the pointer 340 of said potentiometer is connected by conductor 341 to pointer 342 of potentiometer 181, thereby completing the ydirect lcurrent circuit from the regulator tube 328 to rectifier 180.

The conductor 344 has connection at 345 to the negative conductor 182 `of the twelve-phase rectifier 180 and said conductor 344 has also a center-tap connection 346 to each of the secondary windings 261, 280 land 301. This connection of the rectifier to the grid circuits of the electronic tubes 266, 285 and 306 -functions to add the direct current component of the synthesized waveforms Ito the alternating current component which is produced in the split secondary windings 261, 280 and 301 Iby the cathode lfol-lower tubes, lall yas described. It will also ybe understood lthat the direct current voltage obtained from regulator tube G28 and which is 'adjustable in value by means of the voltage divider and potentiometer 338, is `applied to the grid-cathode circuit of the tubes 266, 285 and 306. Thus the same provides the level on the synthesized waveforms `at which the tubes will conduct and is the means yfor setting the desired firing points.

Reference is made to FIGURE 5 for an illustration of the transformer arrangement for supplying the firing pulses .to the ignitrons and the threeaphase welding machine. The transformers 275, 277, 293, 297, 813 and 317 are provided with secondary windings design-ated, respectively, by numerals 348, 349, 350, 351, 352 `and 353. lA resistor such ias 354 is connected across the terminals of each secondary winding and one end of each winding is connected to the common conductor 355 having the output terminal 356. The other output terminal for sec- .ondary winding 348 is indicated by numeral 357 and for the remaining windings by the numerals 358 and 362, respectively. The pulses produced in windings 348 and 349 relate back to the primary winding 161 of the polyaplrase transformer 160. Assuming that the pulse in 348 is positive, then -a positive pulse will be produced in 349 one hundred and eighty degrees later. The phase shift setting for the voltage compensating circuit, namely, the direct current reference level, will determine the instant in the half cycles of the line voltages, at which the pulses in 348 'and 349 will occur, the said phase shifting being continuous and lautomatically compensating for voltage changes in the poly-phase power supply. In a similar manner the pulses produced in windings 350 and V351 rel-ate back to Winding 162 of the transformer 160 and are phase shifted in like manner, and if the pulse in 350 is positive at a particular time, then the pulse in 351 will be positive 4and one hundred and eighty degrees later. Likewise, for windings 352 and 353 the pulses developed therein are also similarly phase shifted yand occur in the same time relation land they relate back to primary Winding 163 of transformer 160. In the operation of a threephase welding machine it should be understood that the positive pulses for windings 348, 350 and 352 will be employed in 4a manner to produce a unidirectional welding current -and following the same the next welding current is produced by employing the positive pulses from windings 349, 351 land 353.

This application is Ia division of my copending application Serial No. 777,774, tiled December 2, 1958v and entitled Automatic Voltage Compensator, now abancloned.

The invention is not to be limited to or by details of construction of the particular embodiment thereof illustrated by the drawings yas various `other forms of the device will of `course be `appa-rent to those skilled in the art without departing from the spirit of the invention or the scope of the claims.

What is claimed is:

l. In a voltage compensating circuit, the combination with a polyaphase alternating current supply, of a dualt-riode electric valve for each phase having a primary winding connected to the `cathodes thereof and having a resistance-capacity network connected to each grid, means coupling the grid-cathode circuits of each valve with its respective phase of the alternating current supply and in a manner whereby each valve will have push-pull operation so that the primary winding having yconnection with each valve will be center tapped providing two sections, means rectifying the poly-phase alternating current to produce a direct `current voltage which will Vary in magnitude as the voltages of the alternating current supply may vary, a second group of dual-triode electric valves including one for each phase, a secondary winding inductively associated with each said primary winding and having connection with the grids of 'a valve of the second group, means connecting the rectifier to the grid-'cathode circuits of the second group of valves including a conductor having a center-tapped relation with each secondary winding to provide two sections respectively, a primary winding in each plate-cathode ycircuit of said second group of valves and wherein phase-shifted electric pulses are produced las a result of operation of the valves, 4and a regulator valve 'capable of producing a direct current voltage and which is Ialso supplied to the grid-cathode circuits of the second group of valves for setting a voltage level in excess of which the valves will conduct.

l2. In a voltage compensating circuit as defined by claim l, wherein the regulator valve will deliver a direct current voltage which will be relatively constant, and additionally including a voltage divider resistance network for adjusting the direct current voltage output of the regulator valve as supplied to the grid-cathode circuits ofthe second group of valves.

3. In a voltage compensating circuit, the combination with a poly-phase alternating current supply, of a dual-.triode electric Valve for each phase having a primary Winding in series circuit with the cathodes thereof and having a resistance-capacity network connected to each grid, inductive means in the form of a winding for each phase and which lhave a star-connected relation, a conductor joining each resistance-capacity network with an end of a winding and another conductor joining the star connection of the inductive means with the primary windings respectively in a manner to center-tap the same whereby the valves are connected for push-pull operation, means rectifying the poly-phase Ialternating current to produce a direct current voltage which will vary in magnitude as the voltages of the alternating current supply may vary, a second group of dual-triode electric Valves including one for each phase, a secondary winding inductively associated with each said primary winding and having connection with the grids of a valve of the second group, means connecting the rectifier in the gridcathode circuits of the second group of valves including a conductor having a center-tapped relation with each secondary winding to provide two sections, a primary winding in each plate-cathode circuit of said second group of valves and wherein phase-shifted electric pulses are produced as a result of conduction of the valves, and a regulator valve capable of producing `a direct current voltage and which is also Supplied to the grid-cathode circuits of the second group of valves for setting a voltage level in excess of which the valves will conduct.

4. In a voltage compensating circuit for three-phase alternating current, the combination with transformer structure having three delta-connected primary windings, at least two sets of delta-connected secondary windings and a third set of star-connected secondary windings, of a rectilier, connections between the rectifier and the said sets of delta-connected secondary windings so arranged as to rectify the alternating currents induced in the secondary windings in a manner to produce a direct current voltage having a ripple of low amplitude and high frequency and which will vary in magnitude as the voltages of the alternating current source may vary, a plurality of dual-triode electric valves each having a primary winding in electrical connection with the cathodes thereof, conductors connecting the windings of the star-connected secondary and the said primary windings yof the valves to form the grid-cathode circuits of said valves respectively to thereby connect them for push-pull operation, certain of said conductors including a resistancecapacity network, a secondary winding in inductive relation with each primary winding of said valves, a pair of electric valves for each secondary winding, conductors connecting the grids of said last mentioned electric valves to the secondary windings respectively, a primary winding in each plate-cathode circuit of each last mentioned elec- .tric valve and wherein phase-shifted electric pulses are produced upon operation of its particular valve, a conductor having a center-tapped relation with each secondary winding, said conductors being joined to said rectifier for supplying the rectied voltage to the grid-cathode circuits of the last mentioned electric valves, and biasing means for the grids of said last mentioned electric valves for setting a direct current voltage level in excess of which the said valves are caused to become conductive.

5. In a voltage compensating circuit, the combination with Ia source of three-phase alternating current voltage, of a transformer having three delta-connected primary windings connected across respective phases of the source, a plurality of sets of secondary windings for said transformer, a rectier, connections between the rectilier and at least two sets of secondary windings for rectifying the alternating currents induced in the secondary windings whereby to produce a direct curr-ent voltage, the magnitude of which will vary as the voltages of the alternating current source may vary, the third set of secondary windings being star-connected, a plurality of dualtriode electric valves each having a center-tapped primary winding in electrical connection with the cathodes thereof, connections between the windings `of the star-connected secondary, the center-.tap of said primary windings and the grids of said electric valves, respectively, thereby connecting each valve for push-pull operation, certain connections including a resistance-capacity i'ilter, a centertapped secondary winding in inductive relation with each center-tapped primary winding, a dual-triode electric valve for each secondary winding, conductors connecting the grids of said last mentioned electric valves with the said secondary windings, respectively, a primary winding 1n each plate-cathode circuit of each last mentioned electric valve and wherein phase-shifted electric pulses are produced when conduction occurs in its triode section, a conductor having a center-tapped rela-tion with each last mentioned secondary winding, said conductor being joined to the said rectifier for supplying the rectified voltage to the grid-cathode circuits of the last mentioned electric valves, and means including a regulator valve capable of delivering a constant direct current voltage and which is also suppled tothe grid-cathode circuits of said last mentioned electric valves.

6. A method of compensating for voltage variations in the three-phase alternating current supply as delivered to a three-phase welding machine whereby to obtain welding currents having uniform heating effects, the steps which include the rectification of the three voltages of the alternating current supply to produce a direct current voltage which will vary in magnitude as the alternating current voltages may vary, obtaining alternating current voltages from each phase of the supply source by induction, filtering each alternating current voltage and feeding Ithe same to electric valves respectively of a type connected by circuitry -for pushpul1 cathode follower operation, whereby the output of the said cathode follower circuitry comprises the alternating current component of synthesized waveforms as obtained for each phase of the source, combining the outputs of the said cathode follower circuitry with the rectified direct current voltage, the latter comprising the direct current component of the synthesized waveforms, and obtaining from said synthesized waveforms tiring pulses at variable phase angles with respect yto `their particular alternating current supply voltage as determined by the variations in the magnitude of the rectified direct current voltage.

No references cited. 

1. IN A VOLTAGE COMPENSATING CIRCUIT, THE COMBINATION WITH A POLY-PHASE ALTERNATING CURRENT SUPPLY, OF A DUALTRIODE ELECTRIC VALVE FOR EACH PHASE HAVING A PRIMARY WINDING CONNECTED TO THE CATHODES THEREOF AND HAVING A RESISTANCE-CAPACITY NETWORK CONNECTED TO EACH GRID, MEANS COUPLING THE GRID-CATHODE CIRCUITS OF EACH VALVE WITH ITS RESPECTIVE PHASE OF THE ALTERNATING CURRENT SUPPLY AND IN A MANNER WHEREBY EACH VALVE WILL HAVE PUSH-PULL OPERATION SO THAT THE PRIMARY WINDING HAVING CONNECTION WITH EACH VALVE WILL BE CENTER TAPPED PROVIDING TWO SECTIONS, MEANS RECTIFYING THE POLY-PHASE ALTERNATING CURRENT TO PRODUCE A DIRECT CURRENT VOLTAGE WHICH WILL VARY IN MAGNITUDE AS THE VOLTAGES OF THE ALTERNATING CURRENT SUPPLY MAY VARY, A SECOND GROUP OF DUAL-TRIODE ELECTRIC VALVES INCLUDING ONE FOR EACH PHASE, A SECONDARY WINDING INDUCTIVELY ASSOCIATED WITH EACH SAID PRIMARY WINDING AND HAVING CONNECTION WITH THE GRIDS OF A VALVE OF THE SECOND GROUP, MEANS CONNECTING THE RECTIFIER TO THE GRID-CATHODE CIRCUITS OF THE SECOND GROUP OF VALVES INCLUDING A CONDUCTOR HAVING A CENTER-TAPPED RELATION WITH EACH SECONDARY WINDING TO PROVIDE TWO SECTIONS RESPECTIVELY, A PRIMARY WINDING IN EACH PLATE-CATHODE CIRCUIT OF SAID SECOND GROUP OF VALVES AND WHEREIN PHASE-SHIFTED ELECTRIC PULSES AND PRODUCED AS A RESULT OF OPERATION OF THE VALVES, AND A REGULATOR VALVE CAPABLE OF PRODUCING A DIRECT CURRENT VOLTAGE AND WHICH IS ALSO SUPPLIED TO THE GRID-CATHODE CIRCUITS OF THE SECOND GROUP OF VALVES FOR SETTING A VOLTAGE LEVEL IN EXCESS OF WHICH THE VALVES WILL CONDUCT. 